The keyboard has been the input device of choice for entering text and other alphanumeric data (collectively referred to herein as "text") into most computer systems. Experts use "touch-typing" techniques to enter text at relatively high rates, while novices often employ "hunt and peck" techniques to perform the text entry function at more modest rates.
Modern computers permit of many different form factors, some of which are not particularly well matched to the use of a keyboard for text entry purposes. For example, there are very small "pocket size" and even smaller personal computers, as well as computers that have very large (e.g., wall size) user interfaces to facilitate collaborative interaction. In these miniaturized and very large scale computer systems, the keyboard commonly is supplemented or even replaced by an alternative text entry mechanism, such a stylus or similar pointing device, that can be manually manipulated by the user to "handwrite" graphical symbols that represent the desired text, together with an appropriately programmed processor for translating the handwritten symbols into corresponding alphanumeric computer codes.
The challenge, of course, for these interpreted text entry systems is to accurately interpret the handwritten symbols in the face of the graphical variations that may exist among different instances of most any handwritten symbol when each of the instances is written by a different user or even when all of the instances are written by the same user. High speed and/or "eyes free" handwriting tend to make it even more difficult to meet this challenge because they generally detract from the graphical precision with which the symbols are written (i.e., they usually increase the "sloppiness" of the handwriting).
Clearly, the characters of ordinary Roman alphabets are not reliably distinguishable from each other in the face of rapid or otherwise sloppy writing. For example, many pairs of letters in the English alphabet (such as "r" and "v," "a" and "d," "N" and "W," and "g" and "q") tend to blur together when they are written quickly, without paying close attention to their subtle graphical distinctions. Accordingly, it will be evident that the performance of interpreted text entry systems could be improved if all text was entered using characters that are well separated from each other in "sloppiness space."
This "sloppiness space" notion can best be understood by recognizing that each alphanumeric symbol is defined by some number of features (say, d features). Thus, each symbol nominally resides at a unique point in a d-dimensional space which is referred to herein as "sloppiness space." From this it follows that the amount of overlap, if any, that occurs in the positioning within this d-dimensional space of the normal variants of the symbols of a given alphabet determines how well separated those symbols are in sloppiness space. If there is little, if any, overlap between the variants of different symbols, the symbols are "well separated from each other in sloppiness space."
Ordinary shorthand systems are attractive for interpreted text entry because they can be used to write text at high speed. Unfortunately, however, known shorthand systems use symbols that are at least as difficult to recognize as cursive writing. Nevertheless, it should be noted that there are both orthographic and phonetic shorthand systems for writing text at an atomic level (i.e., the character level in the case of orthographic systems and the phoneme level in the case of phonetic systems). As is known, orthographic systems use conventional spelling and have one symbol for each letter of the native alphabet (e.g., the English alphabet). They, therefore, are relatively easy to learn, but they provide only a modest speedup over ordinary cursive. Phonetic systems (such as the well known Gregg and Pitman systems), on the other hand, employ phonetic spelling, and sometimes use special phonetic alphabets to do so. This makes them more difficult to learn, but it also explains why they generally are preferred when speed is of paramount concern. This indicates that there is a trade off between speed and ease of learning that comes into play when designing a stylus compatible alphabet for interpreted text entry systems.